- Original research
- Open Access
Does PRRT with standard activities of 177Lu-octreotate really achieve relevant somatostatin receptor saturation in target tumor lesions?: insights from intra-therapeutic receptor imaging in patients with metastatic gastroenteropancreatic neuroendocrine tumors
© Sabet et al.; licensee Springer. 2013
- Received: 18 September 2013
- Accepted: 4 December 2013
- Published: 26 December 2013
Peptide receptor radionuclide therapy (PRRT) with 177Lu-[DOTA0,Tyr3]octreotate (177Lu-octreotate) is generally performed using a fixed activity of 7.4 GBq (200 mCi) per course bound to 180 to 300 μg of the peptide. While this single activity may lead to suboptimal radiation doses in neuroendocrine tumors (NET) with advanced or bulky disease, dose escalation has been withheld due to concerns on potential tumor somatostatin receptor saturation with reduced efficacy of the added activity. In vivo saturation effects during standard-dose PRRT based on quantification of pre- and intra-therapeutic 68Ga-DOTATOC positron emission tomography (PET) imaging might guide potential dose escalation.
Five patients with metastatic NET of the pancreas underwent 68Ga-DOTATOC PET/CT before and directly after standard-dose PRRT with 177Lu-octreotate. In each patient, four target tumor lesions, normal liver parenchyma, and the spleen were evaluated and the ratios of SUVmax of the target lesions to liver (SUVT/L) and spleen (SUVT/S) were calculated; paired Student's t test was performed with p < 0.05 for pre-/intra-PRRT comparisons.
The mean intra-therapeutic tumor SUVmax showed no significant change (per-lesion paired t test) compared to pretreatment values (-9.1%, p = 0.226). In contrast, the SUVmax of the normal liver parenchyma and spleen were significantly lower directly after infusion of 7.4 GBq 177Lu-octreotate. Consequently, SUVT/L and SUVT/S increased significantly from pretreatment to intra-therapeutic examination: SUVT/L (p < 0.001) from 2.8 ± 1.3 (1.3 to 5.8) to 4.7 ± 3.0 (2.1 to 12.7) and SUVT/S (p < 0.001) from 1.2 ± 0.7 (0.4 to 3.0) to 3.5 ± 1.5 (1.6 to 7.9).
This small retrospective study provides preliminary evidence for the absence of relevant in vivo saturation of somatostatin receptor subtype 2 (sst2) in tumor lesions during PRRT with standard activities of 177Lu-octreotate in contrast to normal tissue (liver, spleen) showing limited receptor capacity. After being confirmed by larger series, this observation will have significant implications for PRRT: (1) Higher activities of 177Lu-octreotate might be considered feasible in patients with high tumor disease burden or clinical need for remission, and (2) striving to reduce the amount of peptide used in standard preparations of 177Lu-octreotate appears futile.
- Positron Emission Tomography
- Tumor Lesion
- Peptide Receptor Radionuclide Therapy
- Normal Liver Parenchyma
- Receptor Saturation
Neuroendocrine tumors (NET) commonly overexpress somatostatin receptors, in particular the subtype 2 (sst2), which are targeted for tumor-directed imaging and therapy [1–4]. 68Ga-labeled somatostatin analogues with high affinity to sst2 such as 68Ga-DOTA-d-Phe1-Tyr3-octreotate or 68Ga-DOTA-d-Phe1-Tyr3-octreotide are widely used for positron emission tomography (PET) imaging of NET [5–7]. The same sst2 ligands coupled to β-emitters 90Y or 177Lu are successfully utilized for targeted radionuclide therapy, peptide receptor radionuclide therapy (PRRT) comprising a well-established, effective systemic treatment modality in patients with inoperable, metastatic gastroenteropancreatic NET (GEP NET) [8–11].
Standard PRRT with 177Lu-[DOTA0,Tyr3]octreotate (177Lu-octreotate) is performed with administration of a fixed activity of 7.4 GBq (200 mCi) per course [12–15]. This amount of activity is usually bound to 180 to 300 μg of the peptide with the chelator DOTA, [DOTA0,Tyr3]octreotate. One argument against dose escalation has been the concern on receptor saturation effects in the tumor lesions leading to reduced uptake and efficacy of the added activity [12, 16–18]. This assumption has left PRRT with 177Lu-octreotate with an upper limit of activity per cycle of 7.4 GBq that until date has not been challenged; to the best of our knowledge, there are no reports of treatment with higher activities. However, it can be expected that this will lead to suboptimal treatment in some patients with more advanced/bulky tumor disease and a clinical need for tumor remission. The objective of this retrospective study was to investigate potential in vivo saturation of somatostatin receptors observed during standard PRRT according to quantification of intra-treatment PET studies.
The local committee on ethics approved this retrospective study, and all subjects had provided prior written informed consent. Pre- and post-treatment 68Ga-DOTATOC PET/CT images of five patients (three women and two men; age range, 47 to 79 years) with histologically confirmed, unresectable, metastatic NET of the pancreas (P-NET) who underwent one cycle of PRRT with 177Lu-octreotate between 2011 and 2012 were studied. All patients fulfilled the general inclusion criteria for PRRT including sufficient tumor uptake (i.e., ≥normal liver uptake) on baseline receptor imaging (68Ga-DOTATOC PET/CT) [19–21].
PRRT was performed with 7.4 GBq (200 mCi) 177Lu-octreotate administered in 30 min according to the standard protocol from Rotterdam. The 177Lu (IDB Holland, Baarle-Nassau, Netherlands) had a specific activity in the approximate range of 100 to 160 GBq/μmol at the time of administration. The peptide labeling [22, 23] was performed such that an apparent specific activity of about 54 GBq/μmol (ratio of activity to the total amount of peptide) was obtained. Positively charged amino acids were coadministered for nephroprotection [12, 24] (lysine 2.5% and arginine 2.5% in 1 L 0.9% NaCl; infusion of 250 mL/h).
Somatostatin receptor PET imaging
DOTATOC was labeled with 68Ga eluted from an in-house 68Ge/68Ga generator following the procedure described by Zhernosekov et al. . All patients underwent pretreatment as well as intra-therapeutic 68Ga-DOTATOC PET/CT: Pretreatment PET/CT was performed 1 to 3 days before PRRT and intra-therapeutic PET/CT during PRRT, with PET tracer injection 30 min after the start of the treatment infusion. To minimize the interfering effects of the time lag between treatment administration and PET tracer injection on quantitative analysis of intra-therapeutic images, 68Ga-DOTATOC was injected on the treatment ward without delay; the time interval between the end of 177Lu-octreotate infusion and 68Ga-DOTATOC injection for intra-therapeutic PET was <1 min. The scans were acquired from the base of the skull to the upper thighs (five to seven bed positions) 30 min after the injection of 200 MBq 68Ga-DOTATOC. The hybrid PET/CT scanner (Biograph 2, Siemens Medical Solutions Inc., Hoffman Estates, IL, USA) consisted of a dual-detector helical CT and a high-resolution PET scanner with a 16.2-cm axial field of view and a lutetium oxyorthosilicate (LSO) crystal detector (6.45 × 6.45 × 25 mm). CT was performed for attenuation correction and anatomical localization using the following parameters: 60 mAs, 130 kV, 0.8 s/tube rotation, slice thickness 5 mm, slice width 5 mm, and table feed 8 mm/s. Immediately following the CT image acquisition, PET data were acquired for 5 min per bed position. The coincidence time resolution was 500 ps with a coincidence window of 4.5 ns. The sensitivity was 5.7 cps/kBq at 400 keV. The attenuation-corrected PET data were reconstructed using a standardized ordered-subset expectation maximization (OSEM) iterative reconstruction with two iterations and eight subsets and a 5-mm Gaussian filter.
Image analysis and statistical methods
The standardized uptake value (SUV) was determined as a measure of DOTATOC uptake. In each patient, three liver metastases with unimpaired delineation from other sources of tracer accumulation along with the primary tumor or an extrahepatic metastasis if the primary was resected were selected as target lesions, and normal liver parenchyma as well as the spleen (if not affected by tumor infiltration) as background control. Irregular regions of interest with a threshold of 50% of the SUVmax were drawn and the respective SUVs were recorded. In order to normalize tumor SUVs, the ratios of SUVmax of the target lesions to maximal hepatic uptake (SUVT/L) and maximal splenic uptake (SUVT/S) were calculated in pre- and post-treatment 68Ga-DOTATOC PET/CT images. Paired Student's t test was performed with a significance level of p < 0.05 to examine the changes in receptor status after administration of 177Lu-octreotate. The statistical software package SPSS (version 20, SPSS Inc., Chicago, IL, USA) was used to analyze the data.
SUV parameters of 68 Ga-DOTATOC PET imaging before and directly after administration of PRRT with 7.4 GBq 177 Lu-octreotate
SUV max(mean ± SD)
p value a
22.5 ± 8.5
20.0 ± 10.4
8.5 ± 2.5
4.8 ± 2.0
21.4 ± 8.9
5.6 ± 0.8
2.8 ± 1.3
4.7 ± 3.0
1.2 ± 0.7
3.5 ± 1.5
This small retrospective study with 20 analyzed tumor lesions in five patients provides preliminary evidence for the absence of relevant in vivo receptor saturation effects regarding the targeted sst2 receptors in tumor lesions during PRRT with standard activities of 177Lu-octreotate. This observation is contrasted by highly significant saturation effects in normal (nontumor) tissue depicted by somatostatin receptor PET imaging.
Binding of labeled or unlabeled somatostatin analogues to the highly overexpressed membranous sst2 in NET triggers a fast and efficient internalization process of the ligand-receptor complex within 2.5 min . In nuclear medicine, this mechanism results in very effective accumulation of intra-cellular radiolabeled peptides and permits successful tumor imaging and targeted radionuclide therapy [27–29]. The 'recycling’ process of the internalized receptors to the plasma membrane is, on the other hand, relatively slow and may take several hours . This results in saturation-like effects whenever infusion of radiolabeled sst2 ligands is preceded by application of labeled or unlabeled ligands and limits the amount of radiolabeled molecules and thus activity to be delivered into the tumor. The 68Ga-DOTATOC uptake in intra-therapeutic PET imaging directly after 177Lu-octreotate administration, i.e., 30 min after the beginning of the radiopeptide infusion, is mediated by the 'unsaturated’ membranous sst2 binding the PET tracer compound; the extent of its uptake is probably not influenced by (if at all present) recently recycled receptors after 177Lu-octreotate infusion. This imaging approach may allow effective in vivo quantification of the (unbound and available) membranous receptor density during PRRT.
Few studies have reported the possible positive effects associated with the presence of high peptide amounts on the uptake of radiolabeled somatostatin analogues in tumor tissues [28, 30–32]. A systematic investigation of the impact of peptide mass on the uptake of 68Ga-DOTATOC in NET revealed a saturable tracer accumulation in normal organs (spleen and liver) after the administration of 50 μg of unlabeled octreotide . In contrast to this, a saturation effect in the tumor tissue was observed only after preloading with considerably higher amounts of unlabeled octreotide (250 or 500 μg). The increase of selective uptake in tumor lesions after injection of 50 μg octreotide in the same study moreover indicated potential up-regulation of tumor somatostatin receptor density by unlabeled octreotide . Similar results have been observed after administration of long-acting somatostatin 14.5 to 11.4 days prior to PET/CT examination . To date, however, radionuclides with high specific activity and relatively low amounts of peptide are suggested for the purpose of PRRT. Consequently, treatment with 177Lu-octreotate is performed with up to 7.4 GBq 177Lu-octreotate to restrict the peptide mass and avoid somatostatin saturation in tumor lesions. The results of our study confirm the absence of relevant receptor saturation in tumor lesions, while at the same time demonstrating a striking saturation in the spleen and liver, during standard treatment with 7.4 GBq 177Lu-octreotate; this finding may encourage dose escalation strategies, such as in patients with higher tumor disease burden.
Application of different somatostatin analogues, octreotide (68Ga-DOTATOC) and octreotate (177Lu-[DOTA0,Tyr3]octreotate), for imaging and treatment may be regarded as one limitation in this study. Considering the predominant affinity of these somatostatin analogues for the same receptor subtype, the sst2, the receptor 'saturation’ after treatment with 177Lu-octreotate may very well be determined using 68Ga-DOTATOC PET. The SUVmax values are in line with reported results of other authors on 68Ga-DOTATOC PET [33, 34]. The main limitation of our study is the small population size (n = 5), which obviously restricts the strength of our conclusions. However, the striking and highly significant increase of tumor-to-background ratios of 68Ga-DOTATOC uptake (SUVT/L and SUVT/S) after 177Lu-octreotate administration with no significant change in the uptake intensity of target lesions (n = 20) clearly indicates receptor saturation of normal tissues with at the same time preserved receptor capacity of tumor lesions during standard treatment with 7.4 GBq 177Lu-octreotate.
Derived from a small series of intra-individual comparison of pre- and intra-therapeutic somatostatin receptor PET imaging, there is no evidence for clinically relevant somatostatin receptor saturation of targeted tumor lesions. For PRRT with standard activities, the tumor receptor capacity of sst2 does not seem to be nearly reached in contrast to the obviously limited receptor-mediated radiopeptide uptake capacity of normal tissue such as the liver and spleen. After being confirmed by larger series, this observation may have important implications for PRRT, in that (1) higher activities of 177Lu-octreotate (>7.4 GBq) might be considered whenever high tumor disease burden or clinical need for remission exceeds toxicity issues and (2) the amount of peptide used in standard preparations of 177Lu-octreotate is viewed as uncritical, i.e. attempts to reduce peptide mass by employing 177Lu of ultrahigh specific activity would appear nonbeneficial.
We thank all coworkers of the Department of Nuclear Medicine involved in the diagnostic and therapeutic management of NET patients, especially the nurses of the therapy unit, without whom our work in this field and the numerous NET publications including the present one would not have been possible.
- Krenning EP, Kwekkeboom DJ, Bakker WH, Breeman WAP, Kooij PPM, Oei HY, van Hagen M, Postema PTE, de Jong M, Reubi JC, Visser TJ, Reijs AEM, Hofland LJ, Koper JW, Lamberts SWJ: Somatostatin receptor scintigraphy with [111In-DTPA-D-Phe1]- and [123I-Tyr3]-octreotide: the Rotterdam experience with more than 1000 patients. Eur J Nucl Med 1993,20(8):716–731.View ArticlePubMedGoogle Scholar
- Reubi JC, Schar JC, Waser B, Wenger S, Heppeler A, Schmitt JS, Mäcke HR: Affinity profiles for human somatostatin receptor subtypes SST1-SST5 of somatostatin radiotracers selected for scintigraphic and radiotherapeutic use. Eur J Nucl Med 2000,27(3):273–282. 10.1007/s002590050034View ArticlePubMedGoogle Scholar
- Reubi JC: Peptide receptors as molecular targets for cancer diagnosis and therapy. Endocr Rev 2003,24(4):389–427. 10.1210/er.2002-0007View ArticlePubMedGoogle Scholar
- Kwekkeboom DJ, Kam BL, van Essen M, Teunissen JJ, Van Eijck CH, Valkema R, de Jong M, de Herder WW, Krenning EP: Somatostatin-receptor-based imaging and therapy of gastroenteropancreatic neuroendocrine tumors. Endocr Relat Cancer 2010,17(1):R53-R73. doi:ERC-09–0078 10.1677/ERC-09–0078 10.1677/ERC-09-0078View ArticlePubMedGoogle Scholar
- Kowalski J, Henze M, Schuhmacher J, Macke HR, Hofmann M, Haberkorn U: Evaluation of positron emission tomography imaging using [68Ga]-DOTA-D Phe(1)-Tyr(3)-Octreotide in comparison to [111In]-DTPAOC SPECT. First results in patients with neuroendocrine tumors. Mol Imaging Biol 2003,5(1):42–48. doi:S1536163203000386 10.1016/S1536-1632(03)00038-6View ArticlePubMedGoogle Scholar
- Gabriel M, Decristoforo C, Kendler D, Dobrozemsky G, Heute D, Uprimny C, Kovacs P, Von Guggenberg E, Bale R, Virgolini IJ: 68Ga-DOTA-Tyr3-octreotide PET in neuroendocrine tumors: comparison with somatostatin receptor scintigraphy and CT. J Nucl Med 2007,48(4):508–518. doi:48/4/508 10.2967/jnumed.106.035667View ArticlePubMedGoogle Scholar
- Ezziddin S, Lohmar J, Yong-Hing CJ, Sabet A, Ahmadzadehfar H, Kukuk G, Biersack HJ, Guhlke S, Reichmann K: Does the pretherapeutic tumor SUV in 68Ga DOTATOC PET predict the absorbed dose of 177Lu octreotate? Clin Nucl Med 2012,37(6):e141-e147. doi:10.1097/RLU.0b013e31823926e5 00003072–201206000–00030 10.1097/RLU.0b013e31823926e5View ArticlePubMedGoogle Scholar
- Imhof A, Brunner P, Marincek N, Briel M, Schindler C, Rasch H, Mäcke HR, Rochlitz C, Müller-Brand J, Walter MA: Response, survival, and long-term toxicity after therapy with the radiolabeled somatostatin analogue [90Y-DOTA]-TOC in metastasized neuroendocrine cancers. J Clin Oncol 2011,29(17):2416–2423. doi:JCO.2010.33.7873 10.1200/JCO.2010.33.7873 10.1200/JCO.2010.33.7873View ArticlePubMedGoogle Scholar
- Kwekkeboom DJ, De Herder WW, Van Eijck CH, Kam BL, Van Essen M, Teunissen JJ, Krenning EP: Peptide receptor radionuclide therapy in patients with gastroenteropancreatic neuroendocrine tumors. Semin Nucl Med 2010,40(2):78–88. doi:S0001–2998(09)00102–0 10.1053/j.semnuclmed.2009.10.004 10.1053/j.semnuclmed.2009.10.004View ArticlePubMedGoogle Scholar
- Ezziddin S, Opitz M, Attassi M, Biermann K, Sabet A, Guhlke S, Brockmann H, Willinek W, Wardelmann E, Biersack HJ, Ahmadzadehfar H: Impact of the Ki-67 proliferation index on response to peptide receptor radionuclide therapy. Eur J Nucl Med Mol Imaging 2011,38(3):459–466. doi:10.1007/s00259–010–1610–2 10.1007/s00259-010-1610-2View ArticlePubMedGoogle Scholar
- Ezziddin S, Sabet A, Heinemann F, Yong Hing CJ, Ahmadzadehfar H, Guhlke S, Höller T, Willinek W, Boy C, Biersack HJ: Response and long-term control of bone metastases after peptide receptor radionuclide therapy with (177)Lu-octreotate. J Nucl Med 2011,52(8):1197–1203. doi:jnumed.111.090373 10.2967/jnumed.111.090373 10.2967/jnumed.111.090373View ArticlePubMedGoogle Scholar
- Kwekkeboom DJ, Bakker WH, Kam BL, Teunissen JJ, Kooij PP, de Herder WW, Feelders RA, van Eijck CH, de Jong M, Srinivasan A, Erion JL, Krenning EP: Treatment of patients with gastro-entero-pancreatic (GEP) tumours with the novel radiolabelled somatostatin analogue [177Lu-DOTA(0), Tyr3]octreotate. Eur J Nucl Med Mol Imaging 2003,30(3):417–422. doi:10.1007/s00259–002–1050–8 10.1007/s00259-002-1050-8View ArticlePubMedGoogle Scholar
- Kwekkeboom DJ, Mueller Brand J, Paganelli G, Anthony LB, Pauwels S, Kvols LK, O'dorisio TM, Valkema R, Bodei L, Chinol M, Maecke HR, Krenning EP: Overview of results of peptide receptor radionuclide therapy with 3 radiolabeled somatostatin analogs. J Nucl Med 2005,46(Suppl 1):62S-66S. doi:46/1_suppl/62SPubMedGoogle Scholar
- Sansovini M, Severi S, Ambrosetti A, Monti M, Nanni O, Sarnelli A, Bodei L, Garaboldi L, Bartolomei M, Paganelli G: Treatment with the radiolabelled somatostatin analog Lu-DOTATATE for advanced pancreatic neuroendocrine tumors. Neuroendocrinology 2013,97(4):347–354. doi:000348394 10.1159/000348394 10.1159/000348394View ArticlePubMedGoogle Scholar
- Bodei L, Cremonesi M, Grana CM, Fazio N, Iodice S, Baio SM, Bartolomei M, Lombardo D, Ferrari ME, Sansovini M, Chinol M, Paganelli G: Peptide receptor radionuclide therapy with (1)(7)(7)Lu-DOTATATE: the IEO phase I-II study. Eur J Nucl Med Mol Imaging 2011,38(12):2125–2135. doi:10.1007/s00259–011–1902–1 10.1007/s00259-011-1902-1View ArticlePubMedGoogle Scholar
- Breeman WA, Kwekkeboom DJ, Kooij PP, Bakker WH, Hofland LJ, Visser TJ, Ensing GJ, Lamberts SW, Krenning EP: Effect of dose and specific activity on tissue distribution of indium-111-pentetreotide in rats. J Nucl Med 1995,36(4):623–627.PubMedGoogle Scholar
- Cescato R, Schulz S, Waser B, Eltschinger V, Rivier JE, Wester HJ, Culler M, Ginj M, Liu Q, Schonbrunn A, Reubi JC: Internalization of sst2, sst3, and sst5 receptors: effects of somatostatin agonists and antagonists. J Nucl Med 2006,47(3):502–511. doi:47/3/502PubMedGoogle Scholar
- Lesche S, Lehmann D, Nagel F, Schmid HA, Schulz S: Differential effects of octreotide and pasireotide on somatostatin receptor internalization and trafficking in vitro. J Clin Endocrinol Metab 2009,94(2):654–661. doi:jc.2008–1919 10.1210/jc.2008–1919 10.1210/jc.2008-1919View ArticlePubMedGoogle Scholar
- Forrer F, Valkema R, Kwekkeboom DJ, De Jong M, Krenning EP: Neuroendocrine tumors. Peptide receptor radionuclide therapy. Best Pract Res Clin Endocrinol Metab 2007,21(1):111–129. doi:S1521–690X(07)00008–5 10.1016/j.beem.2007.01.007 10.1016/j.beem.2007.01.007View ArticlePubMedGoogle Scholar
- Kwekkeboom DJ, Krenning EP, Lebtahi R, Komminoth P, Kos Kudla B, de Herder WW, Plöckinger U, Mallorca Consensus Conference participants; European Neuroendocrine Tumor Society: ENETS Consensus Guidelines for the Standards of Care in Neuroendocrine Tumors: peptide receptor radionuclide therapy with radiolabeled somatostatin analogs. Neuroendocrinology 2009,90(2):220–226. doi:000225951 10.1159/000225951 10.1159/000225951View ArticlePubMedGoogle Scholar
- Zaknun JJ, Bodei L, Mueller-Brand J, Pavel ME, Baum RP, Horsch D, O'Dorisio MS, O'Dorisiol TM, Howe JR, Cremonesi M, Kwekkeboom DJ: The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours. Eur J Nucl Med Mol Imaging 2013,40(5):800–816. doi:10.1007/s00259–012–2330–6 10.1007/s00259-012-2330-6View ArticlePubMedGoogle Scholar
- Breeman WA, De Jong M, Visser TJ, Erion JL, Krenning EP: Optimising conditions for radiolabelling of DOTA-peptides with 90Y, 111In and 177Lu at high specific activities. Eur J Nucl Med Mol Imaging 2003,30(6):917–920. doi:10.1007/s00259–003–1142–0 10.1007/s00259-003-1142-0View ArticlePubMedGoogle Scholar
- Breeman WA, van der Wansem K, Bernard BF, van Gameren A, Erion JL, Visser TJ, Krenning EP, de Jong M: The addition of DTPA to [177Lu-DOTA0, Tyr3]octreotate prior to administration reduces rat skeleton uptake of radioactivity. Eur J Nucl Med Mol Imaging 2003,30(2):312–315. doi:10.1007/s00259–002–1054–4 10.1007/s00259-002-1054-4View ArticlePubMedGoogle Scholar
- Kwekkeboom DJ, Teunissen JJ, Bakker WH, Kooij PP, De Herder WW, Feelders RA, van Eijck CH, Esser JP, Kam BL, Krenning EP: Radiolabeled somatostatin analog [177Lu-DOTA0,Tyr3]octreotate in patients with endocrine gastroenteropancreatic tumors. J Clin Oncol 2005,23(12):2754–2762. doi:23/12/2754 10.1200/JCO.2005.08.066View ArticlePubMedGoogle Scholar
- Zhernosekov KP, Filosofov DV, Baum RP, Aschoff P, Bihl H, Razbash AA, Jahn M, Jennewein M, Rösch F: Processing of generator-produced 68Ga for medical application. J Nucl Med 2007,48(10):1741–1748. doi:jnumed.107.040378 10.2967/jnumed.107.040378 10.2967/jnumed.107.040378View ArticlePubMedGoogle Scholar
- Waser B, Tamma ML, Cescato R, Maecke HR, Reubi JC: Highly efficient in vivo agonist-induced internalization of sst2 receptors in somatostatin target tissues. J Nucl Med 2009,50(6):936–941. doi:jnumed.108.061457 10.2967/jnumed.108.061457 10.2967/jnumed.108.061457View ArticlePubMedGoogle Scholar
- Wild D, Macke HR, Waser B, Reubi JC, Ginj M, Rasch H, Müller-Brand J, Hofmann M: 68Ga-DOTANOC: a first compound for PET imaging with high affinity for somatostatin receptor subtypes 2 and 5. Eur J Nucl Med Mol Imaging 2005,32(6):724. doi:10.1007/s00259–004–1697–4 10.1007/s00259-004-1697-4View ArticlePubMedGoogle Scholar
- Reubi JC, Waser B, Cescato R, Gloor B, Stettler C, Christ E: Internalized somatostatin receptor subtype 2 in neuroendocrine tumors of octreotide-treated patients. J Clin Endocrinol Metab 2010,95(5):2343–2350. doi:jc.2009–2487 10.1210/jc.2009–2487 10.1210/jc.2009-2487View ArticlePubMedGoogle Scholar
- Sharif N, Gendron L, Wowchuk J, Sarret P, Mazella J, Beaudet A, Stroh T: Coexpression of somatostatin receptor subtype 5 affects internalization and trafficking of somatostatin receptor subtype 2. Endocrinology 2007,148(5):2095–2105. doi:en.2006–1266 10.1210/en.2006–1266 10.1210/en.2006-1266View ArticlePubMedGoogle Scholar
- Haug AR, Rominger A, Mustafa M, Auernhammer C, Goke B, Schmidt GP, Wängler B, Cumming P, Bartenstein P, Hacker M: Treatment with octreotide does not reduce tumor uptake of (68)Ga-DOTATATE as measured by PET/CT in patients with neuroendocrine tumors. J Nucl Med 2011,52(11):1679–1683. doi:jnumed.111.089276 10.2967/jnumed.111.089276 10.2967/jnumed.111.089276View ArticlePubMedGoogle Scholar
- Velikyan I, Sundin A, Eriksson B, Lundqvist H, Sorensen J, Bergström M, Långström B: In vivo binding of [68Ga]-DOTATOC to somatostatin receptors in neuroendocrine tumours--impact of peptide mass. Nucl Med Biol 2010,37(3):265–275. doi:S0969–8051(09)00288–1 10.1016/j.nucmedbio.2009.11.008 10.1016/j.nucmedbio.2009.11.008View ArticlePubMedGoogle Scholar
- Dorr U, Rath U, Sautter-Bihl ML, Guzman G, Bach D, Adrian HJ, Bihl H: Improved visualization of carcinoid liver metastases by indium-111 pentetreotide scintigraphy following treatment with cold somatostatin analogue. Eur J Nucl Med 1993,20(5):431–433.View ArticlePubMedGoogle Scholar
- Kroiss A, Putzer D, Uprimny C, Decristoforo C, Gabriel M, Santner W, Kranewitter C, Warwitz B, Waitz D, Kendler D, Virgolini IJ: Functional imaging in phaeochromocytoma and neuroblastoma with 68Ga-DOTA-Tyr3-octreotide positron emission tomography and 123I-metaiodobenzylguanidine: a clarification. Eur J Nucl Med Mol Imaging 2012,39(3):543. doi:10.1007/s00259–011–1962–2 10.1007/s00259-011-1962-2View ArticlePubMedGoogle Scholar
- Boy C, Heusner TA, Poeppel TD, Redmann-Bischofs A, Unger N, Jentzen W, Brandau W, Mann K, Antoch G, Bockisch A, Petersenn S: 68Ga-DOTATOC PET/CT and somatostatin receptor (sst1-sst5) expression in normal human tissue: correlation of sst2 mRNA and SUVmax. Eur J Nucl Med Mol Imaging 2011,38(7):1224–1236. doi:10.1007/s00259–011–1760-x 10.1007/s00259-011-1760-xView ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.